Increased temperatures from climate change and growing urbanization are slowing the development
of some native Ohio butterflies, a new study warns.

This could threaten the number of eastern swallowtails and seven other Ohio natives while
helping to spread invasive butterfly species, said Sarah Diamond, an assistant professor of biology
at Case Western Reserve University and lead author of the study published online in the journal
Ecology.

Researchers disagree on whether this is good or bad, but say the findings could help predict
effects of environmental changes over the next several decades.

“The shifts in life cycle were surprising,” Diamond said. “We’re using butterflies as an
indicator for how other things in the ecosystem might be impacted.”

Diamond analyzed 20 species monitored for 13 years by volunteers with Ohio Lepidopterists, a
society of butterfly enthusiasts.

Volunteers recorded species numbers from the first week of April through the first week of
November at parks across Ohio.

Sites in southern Ohio — which range 2 to 3 degrees warmer than northern sites — simulated the
warming that climate-change models predict for the Midwest this century. Butterflies emerged as
many as three weeks earlier in southern Ohio than in central and northern Ohio.

“They could be advancing their lifecycle events to take advantage of earlier blooming and
flowering,” Diamond said.

But for city dwellers, the added heat from buildings and roads slowed growth by several weeks
for eight species, including the eastern tiger swallowtail, pearl crescent and red admiral.
Butterflies generally emerge around mid-June, Diamond said, but these species were not emerging
until early or mid-July.

“Butterflies need warmth to develop,” she said. “But too much heat — before it kills them — can
cause delays.”

The delays might leave the butterflies with less food and time to reproduce, Diamond said, which
could shrink local populations.

David Parshall, a former president of Ohio Lepidopterists, disagrees. He said urbanization —
replacing fields and flowers with pavement, houses and office buildings — affects butterflies more
than an increase in temperature.

“Even if they are developing later in the year ... species have been evolving for thousands of
years,” Parshall said. “Weather patterns have always been here.”

If some species are emerging later, they’re doing it for an evolutionary reason, he added, so
their numbers shouldn’t suffer.

Invasive species such as the European skipper and cabbage white, which can feed on nectar from a
variety of weeds and flowers, are more likely to thrive, experts say. The skipper is emerging a few
weeks early — in late May — even in the combined heat of climate change and urbanization.

“If you have a generalist feeder, then it’s not going to be an issue because there are lots of
host plants to choose from,” said Norman Johnson, an Ohio State University entomologist and
director of the museum’s Triplehorn insect collection.

“But if you have a specialist that develops too early or late and gets out of sync with its host
plant — that’s going to be bad.”

There’s no proof that butterflies are losing sync with their host plants, but the data suggest
it could be happening, Diamond said.

The spicebush swallowtail, pearl crescent, little wood nymph and eastern tailed blue
butterflies, which all have specific host plants, were among the most delayed, she said. This
suggests they were shifting their lifecycles to try to track their host plants.

“Since it’s harder to track a single plant species rather than an entire suite of different
species that butterflies can choose among, there is greater potential for asynchrony in specialist
butterflies,” Diamond said.

And because these specialists are shifting toward emerging later in the year rather than
earlier, they’re losing a competitive edge.

“There’s also the potential for predators that butterflies usually don’t encounter suddenly
co-occurring with them,” Diamond said, which could disrupt the food chain.

The shifts in development will likely expand.

“Our projections are current levels of urbanization and projected climate change over the next
50 or so years, but obviously the climate will continue to warm,” she said. “I think there is
potential for exacerbation of these impacts.”

Diamond said her findings are applicable nationwide, though Ohio has the most intensive
butterfly-monitoring records in the United States.

The next phase of research will include setting up growth chambers in her lab to simulate
environmental conditions, such as climate change and urbanization, to track temperature
triggers.